N-bromobutanimide → 4-(Bromomethyl)-N-[(dimethylamino)sulfonyl]-2,5-difluorobenzamide

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A mixture of N-[(dimethylamino)sulfonyl]-2,5-difluoro-4-methylbenzamide (Preparation 2, 0.50 g, 1.80 mmol), N-bromosuccinimide (freshly recrystallised and dried, 0.42 g, 2.34 mmol) and azobisisobutyronitrile (14.8 mg, 0.09 mmol) in 1,2-dichloroethane (15 mL) was heated under reflux with stirring whilst being irradiated with light from a 100 watt lamp. After 6 hours more N-bromosuccinimide (300 mg, 1.69 mmol) and azobisisobutyronitrile (10 mg, 0.06 mmol) were added and the mixture heated for a further 4 hours. An additional amount of N-bromosuccinimide (100 mg, 0.56 mmol) was then added and the mixture heated under reflux for a further 4 hours. The reaction mixture was cooled to room temperature and evaporated in vacuo to leave a pale yellow oil (0.54 g). Purification by silica gel column chromatography eluting with ethyl acetate/heptane 0:100-1:4 afforded the title compound (0.176 g, 27%) as a colourless oil which solidified on standing.

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